1. Field of the Invention
The present invention relates to the use of certain catalyzed hydrazine compositions to reduce chromium(VI) to chromium(III).
2. Description of the Prior Art
Hydrazine (H.sub.2 H.sub.4) is one of the basic inorganic chemicals. It is precursor to numerous chemicals. Furthermore, it has many uses itself. In particular, one known use is to reduce chromium in the hexavalent state, Cr(VI), to Cr(III). This reaction is necessary to remove chromium contaminants, such as chromic acid or dichromate salts, from waste streams by filtration. See Olin Corporation Application Data Sheet entitled "Hydrazine For chromium(VI) Reduction" published in 1981. One specific application is to remove hexavalent chromium from aqueous sodium chlorate solutions. See U.S. Pat. No. 4,268,486, which issued on May 19, 1981, to Noack and Manke. This patent is incorporated herein by reference in its entirety.
The above-cited prior art processes are generally effective for removing hexavalent chromium from aqueous solutions; however, they have one slight drawback. The use of uncatalyzed hydrazine as a reducing agent of Cr(VI) proceeds slower than desired at a neutral pH. This relative rate of reaction raises the cost of employing hydrazine in those instances.
Separately, catalyzed hydrazine compositions have been used for many applications [although not for the reduction of Cr(VI) ions]. One use is as an oxygen scavenger in boiler systems. See U.S. Pat. No. 4,079,018, which issued to Noack on Mar. 14, 1978. This patent is incorporated herein by reference in its entirety.